European Patent Application No. 100119 discloses a process for the epoxidation of olefinic compounds, starting from olefins and hydrogen peroxide or substances which can produce hydrogen peroxide under the reaction conditions, wherein the catalyst is a synthetic zeolite containing titanium atoms (titaniumsilicalite) corresponding to the general formula: EQU TiO.sub.2.(1-`)SiO.sub.2
wherein x is in the range of from 0.0001 to 0.04. The catalyst is chosen from among catalyst compositions having the following molar ratios of reactants:
______________________________________ Molar Ratios of Reactants Preferred Molar Ratios ______________________________________ SiO.sub.2 /TiO.sub.2 5-200 35-65 OH.sup.- /SiO.sub.2 0.1-1.0 0.3-0.6 H.sub.2 O/SiO.sub.2 20-200 60-100 Me/SiO.sub.2 0.0-0.5 0 RN.sup.+ /SiO.sub.2 0.1-2.0 0.4-1.0 ______________________________________
wherein R.sup.+ represents an organic nitrogen cation derived from the organic base utilized for the preparation of titanium-silicalite (TS-1). Me is an alkaline ion, preferably chosen from among Na or K.
The final TS-1 product is a composition having the formula x TiO.sub.2.(1-x)SiO.sub.2 wherein x is in the range of from 0.0001 to 0.04, preferably from 0.01 to 0.025. TS-1 is silicalite-type product wherein titanium atoms vicariate the silicon atoms. A further and more precise identification of the titanium-silicalite which is used as a catalyst is set forth in said European patent application and in Belgian Pat. No. 886812.
The titanium-silicalite catalyst may be utilized in the epoxidation reaction as a dust or preferably in the form of granules having a particle size of from 5 to 1000 .mu.m wherein the granules are made of zeolitic crystals bound by a suitable inorganic binder, preferably oligomeric silica.
It has been observed that in the synthesis of epoxide compounds derived from olefins and hydrogen peroxide with said catalysts in a protic medium (such as water, alcohol and mixtures thereof), selectivity of the desired epoxide is generally very high. Yet some amount of by-products from hydrolysis is always present, especially when working at high temperatures. This results in increased costs because of the lower yield of the epoxide and because of the need to separate the by-products from the reaction.
It has surprisingly been found that it is possible to significantly reduce the amount of the aforesaid undesirable by-products by treating the catalyst prior to the reaction or during the reaction with suitable acid neutralizing agents to neutralize acid groups which are on the catalyst surface. The catalyst can also be treated with a substance which can neutralize catalyst acidity using an inert group bound to a polar group which is easily displaced by reaction with SiOH.
The acidity of non-treated titanium-silicalite is already very low which is due to the presence of some SiOH groups, especially on the outer surface of the crystals or in the lattice defects. However, the presence of even a small number of acid groups results in the production of unacceptable amounts of by-products due to the hydrolysis reaction described above.